1. Field of the Invention
This invention relates to an apparatus for determining a failure of wheel speed sensors that detect wheel speeds of respective wheels of a vehicle for control of torques transmitted to at least two of the wheels.
2. Description of the Prior Art
Conventionally, it is well-known to control torques transmitted to wheels in dependence on the wheel speeds of respective wheels detected by wheel speed sensors of the vehicle. For instance, Japanese Laid-Open Patent Publication (Kokai) No. 6-72171 discloses a technique concerning a torque distribution system for a four-wheel drive vehicle. According to this technique, the engagement force of a clutch which changes the torque distribution between front and rear wheels is controlled depending on the wheel speeds of the four front and rear wheels detected by the wheel speed sensors. More specifically, wheel speed signals indicative of the respective wheel speeds sensed by the wheel speed sensors are input to a 4WD-ECU, together with a steering angle signal from a steering angle signal sensor and a yaw rate signal from a yaw rate sensor. The 4WD-ECU controls the engagement force of the clutch in response to these parameter signals.
Further, if abnormality of the wheel speed sensors is detected, an alarm is issued by the control operation of the 4WD-ECU for notifying the user of the abnormality of the wheel speed sensors, and the engagement force of the clutch is set to such a value as will make stable the behavior of the vehicle, whereby traveling stability of the vehicle is ensured even if abnormality of the wheel speed sensors has occurred.
In this conventional torque distribution system, however, the wheel speed sensors and the 4WD-ECU are generally connected by using a harness. This sometimes causes all the wheel speed signal values delivered from the wheel speed sensors to assume the same value xe2x80x9c0xe2x80x9d upon occurrence of disconnection of a coupler of the harness or the breaking of a wire. Further, such a state in which the wheel speed signal values all assume the value xe2x80x9c0xe2x80x9d of course occurs when the vehicle is actually standing as well. In the conventional torque distribution system, however, the method of distinguishing between causes of this state has not yet been established, that is, a method has not yet been established for determining whether the above state is caused by an actually stopped state of the vehicle or by a failure of the wheel speed sensors due to disconnection of the coupler of the harness or the like. This can result in an erroneous determination of normality/abnormality of the wheel speed sensors.
It is an object of the invention to provide an apparatus for determining a failure of wheel speed sensors that detect wheel speeds of respective wheels of a vehicle, which is capable of properly determining whether or not a wheel speed detection system including the wheel speed sensors has failed when any of wheel speeds detected by the wheel speed sensors indicates a stopped state of a corresponding wheel.
To attain the above object, the invention provides a apparatus for determining a failure of a wheel speed detection system of an automotive vehicle including an internal combustion engine, an automatic transmission having a torque converter, and a plurality of wheels, the wheel speed detection system including a plurality of wheel speed sensors for detecting respective wheel speeds of the plurality of wheels, for control of torques transmitted to at least two of the plurality of wheels via the automatic transmission.
The apparatus according to the invention comprising:
engine rotational speed detection means for detecting a rotational speed of the engine;
input-output rotational speed ratio calculation means for calculating an input-output rotational speed ratio of the torque converter based on an input rotational speed and an output rotational speed of the torque converter;
shift range detection means for detecting a shift range of the automatic transmission;
traveling state determination means for determining whether or not the vehicle is traveling, based on the detected engine rotational speed and the calculated input-output rotational speed ratio when the shift range detected by the shift range detection means is a traveling range; and
sensor failure determination means for determining that the wheel speed detection system has failed if it is determined by the traveling state determination means that the vehicle is traveling, and at the same time, at least one of the plurality of wheel speed sensors indicates a stopped state of a corresponding one of the wheels.
According to this apparatus, the traveling determination means determines whether or not the vehicle is traveling based on the engine rotational speed and the input-output rotational speed ratio of the torque converter when the automatic transmission is in a traveling range. When the vehicle is traveling, the engine rotational speed is in a range of values equal to or greater than a lower limit value to prevent an engine stall. Further, when the automatic transmission is in a traveling range, the rotational speed of an output shaft of the torque converter is in a range of values equal to or greater than a predetermined value since the output shaft is rigidly connected to drive wheels. Therefore, the input-output rotational speed ratio of the torque converter, which is a ratio between the rotational speed of the output shaft and that of an input shaft of the torque converter, i.e., the engine rotational speed, is also in a range of values equal to or larger than a predetermined value. Therefore, by determining whether the vehicle is traveling as described above, it is possible to appropriately determine whether or not the vehicle is actually traveling.
Further, in the apparatus of the invention, when it is determined by the traveling determination means that the vehicle is running, the sensor failure determination means determines that the wheel speed detection system including the wheel speed sensors has failed, on condition that at least one of the wheel speeds detected by the wheel speed sensors indicates a stopped state of a corresponding wheel. This condition or assumed state is an abnormal one in which at least one of the wheel speeds indicates a stopped state of a wheel when the vehicle is actually running. Therefore, by the above failure determination, it is possible to appropriately detect occurrence of a failure of a wheel speed sensor itself, and that of a failure of the wheel speed detection system including the wheel speed sensors, due to disconnection of a coupler of a harness, breaking of a wire, or the like. Further, when the vehicle is actually standing or stopped, this state of the vehicle is properly determined by the traveling determination means, thereby inhibiting the sensor failure determination means from carrying out the failure determination. This makes it is possible to reliably avoid erroneous determination of a failure of the wheel speed sensors, when they are normally operating.
Preferably, the apparatus further includes failure determination inhibition means for inhibiting failure determination by the sensor failure determination means for a predetermined time period after the shift range detection means detects that the shift range of the automatic transmission is switched to the traveling range from a neutral state of the automatic transmission.
Immediately after the automatic transmission has entered the traveling range from the neutral state, stirring of oil in the torque converter increases an amount of change in the input-output rotational speed ratio of the torque converter, thereby making the input-output rotational speed ratio unstable. This can prevent appropriate execution of traveling determination which is carried out based on the unstable input-output rotational speed ratio. Accordingly, as described above, if failure determination by the sensor failure determination means is inhibited for a predetermined time period after the automatic transmission has entered the traveling range from the neutral state, it is possible to eliminate adverse influence of the unstable input-output rotational speed ratio on the failure determination, which makes it possible to reliably prevent erroneous failure determination caused by an erroneous determination of the traveling state of the vehicle.
Preferably, the traveling state determination means includes a table defining a region in which the vehicle is determined to be necessarily traveling, based on a relationship between the engine rotational speed and the input-output rotational speed ratio.
Preferably, when all of the plurality of wheel speed sensors indicate respective stopped states of the plurality of wheels associated therewith, the sensor failure determination means determines that the wheel speed detection system has failed.
Alternatively, or in combination, when any of the plurality of wheel speed sensors indicates a stopped state of a corresponding one of the plurality of wheels, the sensor failure determination means determines that the any of the plurality of wheel speed sensors has failed.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.